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Details: I have a 2001 Nissan Xterra SE

I want to install a house battery into the vehicle. The battery I have been considering is the Universal Battery UB12750. Because this is an AGM battery, and it will be located behind the driver's seat, I'm concerned about overcharging the battery on long trips.

According to the battery specifications, for cyclic use it has a control voltage of 14.6 - 14.8 V. According to the alternator specifications for the Xterra, it has a regulated voltage of 14.1 - 14.7 V. Does this mean that the battery won't overcharge while connected to the main charging system?

Followup question: If there is still a risk of overcharging, would something like this work to protect the battery for my setup? I'm planning on using an isolator either way, but if overcharge protection is an issue I might select this one.

  • Is your intent using the AGM battery behind the seat as a secondary battery in the car? – spicetraders Aug 25 '16 at 22:25
  • @spicetraders Yup. I want to use it as a house battery while camping to power lights, a ham radio, and medical equipment. Being able to self jump if the starter dies would be a nice plus. – Shadow503 Aug 25 '16 at 22:41
  • I prefer the Optima deep cycles. Use one in boat for running navigation, radio, etc. And also have same setup in in Land Cruiser for powering extra lights, GPS and such. – spicetraders Aug 25 '16 at 22:51
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Essentially batteries like the Optima, or Diehard Platinum are AGM batteries. When I was working we used AGM batteries for various purposes on the training range. They were charged by various methods solar, automotive alternators with success.
But the main difference in AGMs made for automotive / marine use, solar use and home use (UB12750) is not in the basic electrical design but in the case design. Home AGMs are much less rugged cases for the most part. So it would best be protected in a battery box with possibly some protective padding.
As for using an isolator most deep cycle isolators have charge protection with automatic charge switching so adding in a regulator in line could stop them from functioning properly. Spend that extra secondary regulator money on a better isolator.

AGM battery tutorials and support

  • Thanks for the info. So are you saying there shouldn't be any risk of overcharge using that battery with my truck (assuming my alternator's voltage regulator is functioning)? Also, I'm not considering adding a second regulator; I'm wondering if the regulation feature of the isolator is necessary or not. I noticed that the one I linked above cuts off above 14.2V, which seems to suggest that it would be off all the time the truck was running! – Shadow503 Aug 25 '16 at 22:52
  • The isolator cutoff at 14.2 means once the main battery is charged then the secondary will charge until it achieves 14.2 volts then will cutoff or go to a trickle. – spicetraders Aug 25 '16 at 22:55
  • I'm still a little confused. Won't the voltage read between 14.1 & 14.7 volts whenever the alternator is running? How would the isolator know the starter battery is charged? – Shadow503 Aug 25 '16 at 23:43
  • The isolator is like your cars regulator, your alternator actually can provide up to some where near 18v, but battery voltage and regulator keeps it in the 14v mid range. Through electronics the isolator separates car battery and second battery and sensing both batteries separately. Charging the car to a normal range using the cars regulator and the second battery to a normal range but it will be on the lower voltage normal range to help with the circuitry being able to work proper. Remember the battery is keeping the voltage down the alternator is trying to raise it up. – spicetraders Aug 26 '16 at 0:11
  • Thanks for all the info. It looks like while some of the pricier models do this, the one I linked and other solenoid based isolators don't have that smart charging feature. So, here's what I'm looking for to accept your answer: 1. Assuming a simple isolator (that connects the house battery when the charging circuit rises above a threshold), is the specified battery safe to use with the specified alternator for long drives (say 12 hours) 2. If the answer to (1.) is no, would the feature linked be enough to protect the AGM battery from overcharging. – Shadow503 Aug 29 '16 at 14:22

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